Words like sedate, grave, and humorless all make no-nonsense sound like a negative word, but I don't think that has to be the case. Same story with no-frills:

austere, spartan, stark

Again, these make no-frills sound like a bad thing. Austere and spartan are rarely used in a complimentary sense.

But I don't think that has to be the case! I know that a no-nonsense car is going to deliver something that's simple and effective. A no-frills car would get me from point A to point B without trying to upsell me on crazy features and trendy marketing.

So, is there a word to describe something that is 'no-nonsense' or 'no-frills' that would put it in a positive light?

Serious is the usual way to describe it. The underlying concept of "no nonsense" is that humor (or any overt evidence of having fun) detracts from important concerns. "No frills" means no decoration, which is from the same anhedonic frame. If what you want is to strip things down to basics, use a different metaphor, like building: foundation, structure, process, design, efficiency, etc.
–
John LawlerMay 3 '14 at 15:10

While there are words for "no-nonsense" and "no-frills", (to the best of my knowledge) they have all picked up negative connotations over the years, Consequently, it would be preferable to use a positive modifier such as "pleasingly" in front of any of the synonyms to negate their unwanted connotations.